Problem: Gabriela had to do problems 25 through 45 for homework tonight. If Gabriela did all of the problems she was assigned, how many problems did she do?
Answer: Instead of counting problems 25 through 45, we can subtract 24 from each number so we instead consider problems 1 through 21. We see that Gabriela did 21 problems. Notice that she did 21 and not 20 problems.